Oxynitride phosphors for use in lighting applications having improved color quality

ABSTRACT

Disclosed are oxynitride phosphor compositions having the formula (RE 1-x Ce x ) 3 Al a-y-z-w Si y Ga z Sc w O 12-y N y , where RE is at least one of Lu, Gd, Y, and Tb, 0.001≦x≦0.10, 0≦w≦2, 0.001≦y≦0.50, 0≦z≦4.999, and 4.5≦a≦5.0. When combined with radiation from a blue or UV LED, these phosphors can provide light sources with good color quality having high CRI over a large color temperature range. Also disclosed are blends of the above oxynitride phosphors and additional phosphors.

BACKGROUND

The present exemplary embodiments relate to novel phosphor compositions.They find particular application in conjunction with convertingLED-generated ultraviolet (UV), violet or blue radiation into whitelight or other colored light for general illumination purposes. Itshould be appreciated, however, that the invention is also applicable tothe conversion of radiation in Hg-based fluorescent lamps, asscintillating detector elements in computed tomography (CT) and positronemission tomography (PET), UV, violet and/or blue lasers, as well asother white or colored light sources for different applications.

Light emitting diodes (LEDs) are semiconductor light emitters often usedas a replacement for other light sources, such as incandescent lamps.They are particularly useful as display lights, warning lights andindicating lights or in other applications where colored light isdesired. The color of light produced by an LED is dependent on the typeof semiconductor material used in its manufacture.

Colored semiconductor light emitting devices, including light emittingdiodes and lasers (both are generally referred to herein as LEDs), havebeen produced from Group III-V alloys such as gallium nitride (GaN). Toform the LEDs, layers of the alloys are typically deposited epitaxiallyon a substrate, such as silicon carbide or sapphire, and may be dopedwith a variety of n and p type dopants to improve properties, such aslight emission efficiency. With reference to the GaN-based LEDs, lightis generally emitted in the UV and/or blue range of the electromagneticspectrum. Until quite recently, LEDs have not been suitable for lightinguses where a bright white light is needed, due to the inherent color ofthe light produced by the LED.

Recently, techniques have been developed for converting the lightemitted from LEDs to useful light for illumination purposes. In onetechnique, the LED is coated or covered with a phosphor layer. Aphosphor is a luminescent material that absorbs radiation energy in aportion of the electromagnetic spectrum and emits energy in anotherportion of the electromagnetic spectrum. Phosphors of one importantclass are crystalline inorganic compounds of very high chemical purityand of controlled composition to which small quantities of otherelements (called “activators”) have been added to convert them intoefficient fluorescent materials. With the right combination ofactivators and host inorganic compounds, the color of the emission canbe controlled. Most useful and well-known phosphors emit radiation inthe visible portion of the electromagnetic spectrum in response toexcitation by electromagnetic radiation outside the visible range.

By interposing a phosphor excited by the radiation generated by the LED,light of a different wavelength, e.g., in the visible range of thespectrum, may be generated. Colored LEDs are often used in toys,indicator lights and other devices. Manufacturers are continuouslylooking for new colored phosphors for use in such LEDs to produce customcolors and higher luminosity.

In addition to colored LEDs, a combination of LED generated light andphosphor generated light may be used to produce white light. The mostpopular white LEDs are based on blue emitting GalnN chips. The blueemitting chips are coated with a phosphor that converts some of the blueradiation to a complementary color, e.g. a yellow-green emission. Thetotal of the light from the phosphor and the LED chip provides a colorpoint with corresponding color coordinates (x and y) and correlatedcolor temperature (CCT), and its spectral distribution provides a colorrendering capability, measured by the color rendering index (CRI).

The CRI is commonly defined as a mean value for 8 standard color samples(R₁₋₈), usually referred to as the General Color Rendering Index andabbreviated as R_(a), although 14 standard color samples are specifiedinternationally and one can calculate a broader CRI (R₁₋₁₄) as theirmean value.

One known white light emitting device comprises a blue light-emittingLED having a peak emission wavelength in the blue range (from about 440nm to about 480 nm) combined with a phosphor, such as cerium dopedyttrium aluminum garnet Y₃Al₅O₁₂: Ce³⁺ (“YAG”). The phosphor absorbs aportion of the radiation emitted from the LED and converts the absorbedradiation to a yellow-green light. The remainder of the blue lightemitted by the LED is transmitted through the phosphor and is mixed withthe yellow light emitted by the phosphor. A viewer perceives the mixtureof blue and yellow light as a white light.

The blue LED-YAG phosphor device described above typically produces awhite light with a general color rendering index (R_(a)) of from about70-82 with a tunable color temperature range of from about 4000K to8000K. Typical general lighting applications require a higher CRI andlower CCT values than possible using the blue LED-YAG approach. In aneffort to improve the CRI, recent commercially available LEDs using ablend of YAG phosphor and one or more additional phosphors, including ared phosphor such as CaS:Eu²⁺ or (Ba, Sr, Ca)₂Si₅N₈:Eu²⁺ to providecolor temperatures below 4000K with a R_(a) around 90.

However, this adds an additional complication in that a phosphor blendis now used, limiting the potential phosphor coating options for thesedevices. In addition, many of the redder phosphors also strongly absorbthe emission from YAG, consquently leading to further losses in theoverall lamp performance.

Thus, there is a continued demand for additional phosphor compositionsthat can be used as a single phosphor component or as part of a phosphorblend in the manufacture of both white and colored LEDs as well as inother applications. Such phosphor compositions will allow an even widerarray of LEDs with desirable properties including the ability to producelight sources with both good color quality (CRI>80) and a large range ofcolor temperatures.

BRIEF DESCRIPTION

In a first aspect, there is provided a rare earth oxynitride phosphorcomprising (RE_(1-x)Ce_(x))₃Al_(a-y-z-w)Si_(y)Ga_(z)Sc_(w)O_(12-y)N_(y),where RE is at least one of Lu, Gd, Y, and Tb, 0.001≦x≦0.10, 0≦w≦2,0.001≦y≦0.50, 0≦z≦4.999, and 4.5≦a≦5.0.

In a second aspect, there is provided a light emitting device includinga semiconductor light source having a peak emission from about 250 toabout 550 nm and a rare earth oxynitride phosphor as defined above.

In a third aspect, there is provided a phosphor blend including a firstrare earth oxynitride phosphor as defined-above and at least oneadditional phosphor, wherein the phosphor blend is capable of emittinglight suitable for use in general illumination either alone or incombination with radiation emitted by a semiconductor light sourceradiationally coupled to the phosphor blend.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic cross-sectional view of an illumination system inaccordance with one embodiment of the present invention.

FIG. 2 is a schematic cross-sectional view of an illumination system inaccordance with a second embodiment of the present invention.

FIG. 3 is a schematic cross-sectional view of an illumination system inaccordance with a third embodiment of the present invention.

FIG. 4 is a cutaway side perspective view of an illumination system inaccordance with a fourth embodiment of the present invention.

FIGS. 5 a-5 d are the emission spectra of several of the presentembodiment phosphors under 470 nm excitation.

FIGS. 6 a-6 b are the diffuse reflectance spectra for(Y_(0.97)Ce_(0.03))₃Al_(4.9)Si_(0.1)O_(11.9)N_(0.1) and(Lu_(0.97)Ce_(0.03))₃Al_(4.8)Si_(0.2)O_(11.8)N_(0.2), respectively.

DETAILED DESCRIPTION

Phosphors convert radiation (energy) to visible light. Differentcombinations of phosphors provide different colored light emissions. Thecolored light that originates from the phosphors provides a colortemperature. Novel phosphor compositions are presented herein as well astheir use in LED and other light sources.

A phosphor conversion material (phosphor material) converts generated UVor blue radiation to a different wavelength visible light. The color ofthe generated visible light is dependent on the particular components ofthe phosphor material. The phosphor material may include only a singlephosphor composition or two or more phosphors of basic color, forexample a particular mix with one or more of a yellow and red phosphorto emit a desired color (tint) of light. As used herein, the term“phosphor material” is intended to include both a single phosphor aswell as a blend of two or more phosphors.

It was determined that an LED lamp that produces a bright-white lightwould be useful to impart desirable qualities to LEDs as light sources.Therefore, in one embodiment of the invention, a luminescent materialphosphor conversion material coated LED chip is disclosed for providingwhite light. The phosphor material may be an individual phosphor or aphosphor blend of two or more phosphor compositions, includingindividual phosphors that convert radiation at a specified wavelength,for example radiation from about 250 to 550 nm as emitted by a UV tovisible LED, into a different wavelength visible light. The visiblelight provided by the phosphor material (and LED chip if emittingvisible light) comprises a bright white light with high intensity andbrightness.

With reference to FIG. 1, an exemplary LED based light emitting assemblyor lamp 10 is shown in accordance with one preferred structure of thepresent invention. The light emitting assembly 10 comprises asemiconductor UV or visible radiation source, such as a light emittingdiode (LED) chip 12 and leads 14 electrically attached to the LED chip.The leads 14 may comprise thin wires supported by a thicker leadframe(s) 16 or the leads may comprise self supported electrodes and thelead frame may be omitted. The leads 14 provide current to the LED chip12 and thus cause the LED chip 12 to emit radiation.

The lamp may include any semiconductor visible or UV light source thatis capable of producing white light when its emitted radiation isdirected onto the phosphor. The preferred peak emission of the LED chipin the present invention will depend on the identity of the phosphors inthe disclosed embodiments and may range from, e.g., 250-550 nm. In onepreferred embodiment, however, the emission of the LED will be in thenear UV to deep blue region and have a peak wavelength in the range fromabout 350 to about 430 nm. Typically then, the semiconductor lightsource comprises an LED doped with various impurities. Thus, the LED maycomprise a semiconductor diode based on any suitable III-V, II-VI orIV-IV semiconductor layers and having an emission wavelength of about250 to 550 nm.

Preferably, the LED may contain at least one semiconductor layercomprising GaN, ZnSe or SiC. For example, the LED may comprise a nitridecompound semiconductor represented by the formula In_(i)Ga_(j)Al_(k)N(where 0≦i; 0≦j; 0≦k and i+j+k=1) having a peak emission wavelengthgreater than about 250 nm and less than about 550 nm. Such LEDsemiconductors are known in the art. The radiation source is describedherein as an LED for convenience. However, as used herein, the term ismeant to encompass all semiconductor radiation sources including, e.g.,semiconductor laser diodes.

Although the general discussion of the exemplary structures of theinvention discussed herein are directed toward inorganic LED based lightsources, it should be understood that the LED chip may be replaced by anorganic light emissive structure or other radiation source unlessotherwise noted and that any reference to LED chip or semiconductor ismerely representative of any appropriate radiation source.

The LED chip 12 may be encapsulated within a shell 18, which enclosesthe LED chip and an encapsulant material 20. The shell 18 may be, forexample, glass or plastic. Preferably, the LED 12 is substantiallycentered in the encapsulant 20. The encapsulant 20 is preferably anepoxy, plastic, low temperature glass, polymer, thermoplastic, thermosetmaterial, resin or other type of LED encapsulating material as is knownin the art. Optionally, the encapsulant 20 is a spin on glass or someother high index of refraction material. Preferably, the encapsulantmaterial 20 is an epoxy or a polymer material, such as silicone. Boththe shell 18 and the encapsulant 20 are preferably transparent orsubstantially optically transmissive with respect to the wavelength oflight produced by the LED chip 12 and a phosphor material 22 (describedbelow). In an alternate embodiment, the lamp 10 may only comprise anencapsulant material without an outer shell 18. The LED chip 12 may besupported, for example, by the lead frame 16, by the self supportingelectrodes, the bottom of the shell 18, or by a pedestal (not shown)mounted to the shell or to the lead frame.

The structure of the illumination system includes a phosphor material 22radiationally coupled to the LED chip 12. Radiationally coupled meansthat the elements are associated with each other so radiation from oneis transmitted to the other.

This phosphor material 22 is deposited on the LED 12 by any appropriatemethod. For example, a water based suspension of the phosphor(s) can beformed, and applied as a phosphor layer to the LED surface. In one suchmethod, a silicone slurry in which the phosphor particles are randomlysuspended is placed around the LED. This method is merely exemplary ofpossible positions of the phosphor material 22 and LED 12. Thus, thephosphor material 22 may be coated over or directly on the lightemitting surface of the LED chip 12 by coating and drying the phosphorsuspension over the LED chip 12. Both the shell 18 and the encapsulant20 should be transparent to allow light 24 to be transmitted throughthose elements. Although not intended to be limiting, in one embodiment,the median particle size of the phosphor material may be from about 1 toabout 10 microns.

FIG. 2 illustrates a second preferred structure of the system accordingto the preferred aspect of the present invention. The structure of theembodiment of FIG. 2 is similar to that of FIG. 1, except that thephosphor material 122 is interspersed within the encapsulant material120, instead of being formed directly on the LED chip 112. The phosphormaterial (in the form of a powder) may be interspersed within a singleregion of the encapsulant material 120 or, more preferably, throughoutthe entire volume of the encapsulant material. Radiation 126 emitted bythe LED chip 112 mixes with the light emitted by the phosphor material122, and the mixed light appears as white light 124. If the phosphor isto be interspersed within the encapsulant material 120, then a phosphorpowder may be added to a polymer precursor, loaded around the LED chip112, and then the polymer precursor may be cured to solidify the polymermaterial. Other known phosphor interspersion methods may also be used,such as transfer loading.

FIG. 3 illustrates a third preferred structure of the system accordingto the preferred aspects of the present invention. The structure of theembodiment shown in FIG. 3 is similar to that of FIG. 1, except that thephosphor material 222 is coated onto a surface of the shell 218, insteadof being formed over the LED chip 212. The phosphor material ispreferably coated on the inside surface of the shell 218, although thephosphor may be coated on the outside surface of the shell, if desired.The phosphor material 222 may be coated on the entire surface of theshell or only a top portion of the surface of the shell. The radiation226 emitted by the LED chip 212 mixes with the light emitted by thephosphor material 222, and the mixed light appears as white light 224.Of course, the structures of FIGS. 1-3 may be combined and the phosphormay be located in any two or all three locations or in any othersuitable location, such as separately from the shell or integrated intothe LED.

In any of the above structures, the lamp 10 may also include a pluralityof scattering particles (not shown), which are embedded in theencapsulant material. The scattering particles may comprise, forexample, Al₂O₃ particles such as alumina powder or TiO₂ particles. Thescattering particles effectively scatter the coherent light emitted fromthe LED chip, preferably with a negligible amount of absorption.

As shown in a fourth preferred structure in FIG. 4, the LED chip 412 maybe mounted in a reflective cup 430. The cup 430 may be made from orcoated with a reflective material, such as alumina, titania, or otherdielectric powder known in the art. A preferred reflective material isAl₂O₃. The remainder of the structure of the embodiment of FIG. 4 is thesame as that of any of the previous Figures, and includes two leads 416,a conducting wire 432 electrically connecting the LED chip 412 with thesecond lead, and an encapsulant material 420.

In one embodiment, the invention provides a novel phosphor composition,which may be used in the phosphor composition 22 in the above describedLED light, wherein the composition is a rare earth oxynitride phosphorcomposition having a formula(RE_(1-x)Ce_(x))₃Al_(a-y-z-w)Si_(y)Ga_(z)Sc_(w)O_(12-y)N_(y), where REis at least one of Lu, Gd, Y, and Tb, 0.001≦x≦0.10, 0≦w≦2, 0.001≦y≦0.50,0≦z≦4.999, and 4.5≦a≦5.0. Preferably, 0.01≦y≦0.05, 0.02≦y≦0.20, 0≦w≦0.5,0≦z≦0.5, and 4.8≦a≦5.0. Even more preferably, 0.05≦y≦0.20.

Preferred phosphors in this embodiment include(Lu_(0.97)Ce_(0.03))₃Al_(4.8)Si_(0.2)O_(11.8)N_(0.2),(Lu_(0.97)Ce_(0.03))₃Al_(4.9)Si_(0.1)O_(11.9)N_(0.1),(Y_(0.97)Ce_(0.03))₃Al_(4.9)Si_(0.1)O_(11.9)N_(0.1), and(Y_(0.97)Ce_(0.03))₃Al_(4.8)Si_(0.2)O_(11.8)N_(0.2).

FIGS. 5 a-5 d are the emission spectra of the above phosphors under 470nm excitation. FIGS. 6 a-6 b are the diffuse reflectance spectra for(Y_(0.97)Ce_(0.03))₃Al_(4.9)Si_(0.2)O_(11.9)N_(0.2) and(Lu_(0.97)Ce_(0.03))₃Al_(4.8)Si_(0.2)O_(11.8)N_(0.2), respectively.

The use of Ce³⁺ as a dopant may increase the efficiency of the resultinglighting device when other phosphors are present. That is, because Eu²⁺doped phosphors are known to absorb the radiation emitted by otherphosphors present in the device while Ce³⁺ typically does not, this hasthe additional benefit of increasing the device package efficiency whenadditional phosphors are present (such as YAG), since less of the lightemitted by these phosphors will be absorbed due to the lowerconcentration of Eu²⁺. In one embodiment, the Ce³⁺ doping levels mayrange from about 0.01 to about 30 mol % replacement.

While suitable in many applications alone with a blue or UV LED chip,the above described oxonitride phosphor may be blended with one or moreadditional phosphors for use in LED light sources. Thus, in anotherembodiment, an LED lighting assembly is provided including a phosphorcomposition comprising a blend of a phosphor from one of the aboveembodiments with one or more additional phosphors. These phosphors canbe used either individually for single color lamps or in blends withother phosphors to generate white light for general illumination. Thesephosphors can be blended with suitable phosphors to produce a whitelight emitting device with CCTs ranging from 2500 to 10,000 K and CRIsranging from 50-99. Non-limiting examples of suitable phosphors for usewith the present inventive phosphors in phosphor blends are listedbelow.

The specific amounts of the individual phosphors used in the phosphorblend will depend upon the desired color temperature. The relativeamounts of each phosphor in the phosphor blend can be described in termsof spectral weight. The spectral weight is the relative amount that eachphosphor contributes to the overall emission spectrum of the device. Thespectral weight amounts of all the individual phosphors and any residualbleed from the LED source should add up to 100%. In a preferredembodiment of blended phosphors, the above described phosphor in theblend will have a spectral weight ranging from about 1 to 75%.

Non-limiting examples of suitable phosphors that may be used incombination with the present oxonitridosilicate phosphors include:

-   (Ba, Sr, Ca)₅(PO₄)₃(Cl, F, Br, OH):Eu²⁺, Sb³⁺-   (Ba, Sr, Ca)MgAl10O₁₇:Eu²⁺,Mn²⁺-   (Ba, Sr, Ca)BPO₅:Eu²⁺, Mn²⁺-   (Sr, Ca)₁₀(PO₄)₆*nB₂O₃:Eu²⁺-   Sr₂Si₃O_(8*2)SrCl₂:Eu²⁺-   Ba₃MgSi₂O₈:Eu²⁺-   Sr₄Al₁₄O₂₅:Eu²⁺-   BaAl₈O₁₃:Eu²⁺-   2SrO*0.84P₂O₅*0.16B₂O₃:Eu²⁺-   (Ba, Sr, Ca)MgAl₁₀O₁₇:Eu²⁺,Mn²⁺-   (Ba, Sr, Ca, Zn)₅(PO₄)₃(Cl, F, OH):Eu²⁺,Mn²⁺, Sb³⁺-   (Ba, Sr, Ca)MgAl₁₀O₁₇:Eu²⁺,Mn²⁺(BAMn)-   (Ba, Sr, Ca)Al₂O₄:Eu²⁺-   (Y, Gd, Lu, Sc, La)BO₃:Ce³⁺, Tb³⁺-   Ca₈Mg(SiO₄)₄Cl₂:Eu²⁺,Mn²⁺-   (Ba, Sr, Ca)₂SiO₄:Eu²⁺-   (Ba, Sr, Ca)₂(Mg, Zn)Si₂O₇:Eu²⁺-   (Sr, Ca, Ba)(Al, Ga, In)₂S₄:Eu²⁺-   (Y, Gd, Tb, La, Sm, Pr, Lu)₃(Al, Ga)₅O₁₂:Ce³⁺-   (Ca, Sr)₈(Mg, Zn)(SiO₄)₄Cl₂:Eu²⁺, Mn²⁺ (CASI)-   Na₂Gd₂B₂O₇:Ce³⁺, Tb³⁺-   (Ba, Sr)₂(Ca, Mg, Zn)B₂O₆:K, Ce, Tb-   (Sr, Ca, Ba, Mg, Zn)₂P₂O₇:Eu²⁺, Mn²⁺ (SPP);-   (Ca, Sr, Ba, Mg)₁₀(PO₄)₆(F, Cl, Br, OH): Eu²⁺, Mn²⁺ (HALO);-   (Gd, Y, Lu, La)₂O₃:Eu³⁺, Bi³⁺-   (Gd, Y, Lu, La)₂O₂S:Eu³⁺, Bi³⁺-   (Gd, Y, Lu, La)VO₄:Eu³⁺, Bi³⁺-   (Ca, Sr)S:Eu²⁺-   SrY₂S₄: Eu²⁺-   CaLa₂S₄:Ce³⁺-   (Ca, Sr)S:Eu²⁺-   3.5MgO*0.5MgF₂*GeO₂:Mn⁴⁺ (MFG)-   (Ba, Sr, Ca)MgP₂O₇:Eu²⁺, Mn²⁺-   (Y,Lu)₂WO₆:Eu³+, Mo⁶⁺-   (Ba, Sr, Ca)_(x)Si_(y)N_(z):Eu²⁺

Preferred phosphors for use in blends with the present oxynitridephosphors include (Sr,Ca)S:Ce³⁺,Eu²⁺;(Sr,Ba,Ca)₂Si_(5-x)Al_(x)N_(8-x)O_(x): Ce³⁺, Eu²⁺; andBaSi₇N₁₀:Ce³⁺,Eu²⁺.

As stated, the inventive phosphors can be used either alone to makesingle color light sources or in blends for white light sources. In onepreferred embodiment, the phosphor composition is a blend of the aboveoxynitride phosphor and one or more gap filling phosphors, such that thelight emitted from the LED device is a white light.

When the phosphor composition includes a blend of two or more phosphors,the ratio of each of the individual phosphors in the phosphor blend mayvary depending on the characteristics of the desired light output. Therelative proportions of the individual phosphors in the variousembodiment phosphor blends may be adjusted such that when theiremissions are blended and employed in an backlighting device, there isproduced visible light of predetermined x and y values on the CIEchromaticity diagram. As stated, a white light is preferably produced.This white light may, for instance, may possess an x value in the rangeof about 0.30 to about 0.55, and a y value in the range of about 0.30 toabout 0.55. As stated, however, the exact identity and amounts of eachphosphor in the phosphor composition can be varied according to theneeds of the end user.

The above described phosphor composition may be produced using knownsolution or solid state reaction processes for the production ofphosphors by combining, for example, elemental nitrides, oxides,carbonates and/or hydroxides as starting materials. Other startingmaterials may include nitrates, sulfates, acetates, citrates, oroxalates. Alternately, coprecipitates of the rare earth oxides could beused as the starting materials for the RE elements. In a typicalprocess, the starting materials are combined via a dry or wet blendingprocess and fired in air or under a reducing atmosphere or in ammonia atfrom, e.g., 1000 to 1600° C.

A fluxing agent may be added to the mixture before or during the step ofmixing. This fluxing agent may be AlF₃, NH₄Cl or any other conventionalfluxing agent, such as a fluoride of at least one metal selected fromthe group consisting of lutetium, yttrium, terbium, aluminum, gallium,and indium. A quantity of a fluxing agent of less than about 20,preferably less than about 10, percent by weight of the total weight ofthe mixture is generally adequate for fluxing purposes.

The starting materials may be mixed together by any mechanical methodincluding, but not limited to, stirring or blending in a high-speedblender or a ribbon blender. The starting materials may be combined andpulverized together in a bowl mill, a hammer mill, or a jet mill. Themixing may be carried out by wet milling especially when the mixture ofthe starting materials is to be made into a solution for subsequentprecipitation. If the mixture is wet, it may be dried first before beingfired under a reducing atmosphere at a temperature from about 900° C. toabout 1700° C., preferably from about 1400° C. to about 1600° C., for atime sufficient to convert all of the mixture to the final composition.

The firing may be conducted in a batchwise or continuous process,preferably with a stirring or mixing action to promote good gas-solidcontact. The firing time depends on the quantity of the mixture to befired, the rate of gas conducted through the firing equipment, and thequality of the gas-solid contact in the firing equipment. Typically, afiring time up to about 10 hours is adequate but for phase formation itis desirable to refire couple of times at the desired temperatures aftergrinding. The reducing atmosphere typically comprises a reducing gassuch as hydrogen, carbon monoxide, ammonia or a combination thereof,optionally diluted with an inert gas, such as nitrogen, helium, etc., ora combination thereof. A typical firing atmosphere is 1% H₂ in nitrogen.Alternatively, the crucible containing the mixture may be packed in asecond closed crucible containing high-purity carbon particles and firedin air so that the carbon particles react with the oxygen present inair, thereby, generating carbon monoxide for providing a reducingatmosphere.

It may be desirable to add pigments or filters to the phosphorcomposition. When the LED is a UV emitting LED, the phosphor layer 22may also comprise from 0 up to about 5 % by weight (based on the totalweight of the phosphors) of a pigment or other UV absorbent materialcapable of absorbing or reflecting UV radiation having a wavelengthbetween 250 nm and 550 nm.

Suitable pigments or filters include any of those known in the art thatare capable of absorbing radiation generated between 250 nm and 550 nm.Such pigments include, for example, nickel titanate or praseodymiumzirconate. The pigment is used in an amount effective to filter 10% to100% of the radiation generated in any of the 250 nm to 550 nm range.

CALCULATED EXAMPLES

The calculated characteristics of LED based lights using a 470 nm LEDchip and various embodiments of the present oxynitride phosphors arelisted below. Phosphor Luminosity (Im/W-opt) CCT CRI(Lu_(0.97)Ce_(0.03))₃Al_(4.8)Si_(0.2)O_(11.8)N_(0.2) 293 3840 83.5(Y_(0.97)Ce_(0.03))₃Al_(4.9)Si_(0.1)O_(11.9)N_(0.1) 285 3100 84(Y_(0.97)Ce_(0.03))₃Al_(4.8)Si_(0.2)O_(11.8)N_(0.2) 292 3480 84

It can be seen that the use of the present phosphors alone can providehigher lights with higher CRI than possible using YAG over a range ofCCT's <4000K with comparable quantum efficiencies.

When used in lighting applications as part of a phosphor blend, byassigning appropriate spectral weights for each phosphor, we can createspectral blends to cover the relevant portions of color space,especially for white lamps. For various desired CCT's, CRI's and colorpoints, one can determine the appropriate amounts of each phosphor toinclude in the blend. Thus, one can customize phosphor blends to producealmost any CCT or color point, with corresponding high CRI. Of course,the color of each phosphor will be dependent upon its exact composition.However, determining the changes in the spectral weight to produce thesame or similar characteristic lighting device necessitated by suchvariations is trivial and can be accomplished by one skilled in the artusing various methodologies, such as design of experiment (DOE) or otherstrategies.

By use of the present invention, single phosphor lamps can be providedhaving CRI values greater than those achievable using YAG alone over awide range of color temperatures. In addition, the use of the presentoxynitride phosphors in LED blends can produce lamps with CRI valuesover 90, over the entire range of color temperatures of interest forgeneral illumination (2500 K to 8000 K). In some blends, the CRI valuesmay approach the theoretical maximum of 100.

The phosphor composition described above may be used in additionalapplications besides LEDs. For example, the material may be used as aphosphor in a Hg fluorescent lamp, in a cathode ray tube, in a plasmadisplay device or in a liquid crystal display (LCD). The material mayalso be used as a scintillator in an electromagnetic calorimeter, in agamma ray camera, in a computed tomography scanner, as scintillatordetector elements in a CT or PET system, or in a laser. These uses aremeant to be merely exemplary and not exhaustive.

The exemplary embodiment has been described with reference to thepreferred embodiments. Obviously, modifications and alterations willoccur to others upon reading and understanding the preceding detaileddescription. It is intended that the exemplary embodiment be construedas including all such modifications and alterations insofar as they comewithin the scope of the appended claims or the equivalents thereof.

1. A lighting apparatus for emitting white light comprising: a lightsource emitting with a peak radiation at from about 250 nm to about 550nm; and a phosphor composition radiationally coupled to the lightsource, the phosphor composition comprising a rare earth oxynitridephosphor comprising(RE_(1-x)Ce_(x))₃Al_(a-y-z-w)Si_(y)Ga_(z)Sc_(w)O_(12-y)N_(y), where REis at least one of Lu, Gd, Y, and Tb, 0.001≦x≦0.10, 0≦w≦2, 0.001≦y≦0.50,0≦z≦4.999, and 4.5≦a≦5.0.
 2. The lighting apparatus of claim 1, whereinthe light source is a semiconductor light emitting diode (LED) emittingradiation having a wavelength in the range of from about 370 to about485 nm.
 3. The lighting apparatus of claim 2, wherein the LED comprisesa nitride compound semiconductor represented by the formulaIn_(i)Ga_(j)Al_(k)N, where 0<i; 0≦j, 0≦K, and i+j+k=1.
 4. The lightingapparatus of claim 1, wherein the light source is an organic emissivestructure.
 5. The lighting apparatus of claim 1, wherein the phosphorcomposition is coated on the surface of the light source.
 6. Thelighting apparatus of claim 1, further comprising an encapsulantsurrounding the light source and the phosphor composition.
 7. Thelighting apparatus of claim 1, wherein the phosphor composition isdispersed in the encapsulant.
 8. The lighting apparatus of claim 1,further comprising a reflector cup.
 9. The lighting apparatus of claim1, wherein said phosphor composition further comprises one or moreadditional phosphor.
 10. The lighting apparatus of claim 9, wherein saidone or more additional phosphors are selected from the group consistingof (Ba, Sr, Ca)₅(PO₄)₃(Cl, F, Br, OH):Eu²⁺, Sb³⁺; (Ba, Sr,Ca)MgAl10O₁₇:Eu²⁺,Mn²⁺; (Ba, Sr, Ca)BPO₅:Eu²⁺, Mn²⁺; (Sr,Ca)₁₀(PO₄)₆*nB₂O₃:Eu²⁺; 2SrO*0.84P₂O₅*016B₂O₃:Eu²⁺;Sr₂Si₃O_(8*2)SrCl₂:Eu²⁺; Ba₃MgSi₂O₈:Eu²⁺; Sr₄Al₁₄O₂₅:Eu²⁺;BaAl₈O₁₃:Eu²⁺; Sr₄Al₁₄O₂₅:Eu²⁺; BaAl₈O₁₃:Eu²⁺;2SrO*0.84P₂O_(5-0.16)B₂O₃:Eu²⁺; (Ba, Sr, Ca)MgAl₁₀O₁₇:Eu²⁺,Mn²⁺; (Ba,Sr, Ca, Zn)₅(PO₄)₃(Cl, F, OH):Eu²⁺, Mn²⁺, Sb³⁺; (Ba, Sr,Ca)MgAl₁₀O₁₇:Eu²⁺,Mn²⁺; (Ba, Sr, Ca)Al₂O₄:Eu²⁺; (Y, Gd, Lu, Sc,La)BO₃:Ce³⁺, Tb³⁺; Ca₈Mg(SiO₄)₄Cl₂:Eu²⁺, Mn²⁺; (Ba, Sr, Ca)₂SiO₄:Eu²⁺;(Ba, Sr, Ca)₂(Mg, Zn)Si₂O₇:Eu²⁺; (Sr, Ca, Ba)(Al, Ga, In)₂S₄:Eu²⁺; (Y,Gd, Tb, La, Sm, Pr, Lu)₃(Al, Ga)₅O₁₂:Ce³⁺; (Ca, Sr)₈(Mg, Zn)(SiO₄)₄Cl₂:Eu²⁺, Mn²⁺ (CASI); Na₂Gd₂B₂O₇:Ce³⁺, Tb³⁺; (Ba, Sr)₂(Ca, Mg, Zn)B₂O₆:K,Ce, Tb; (Sr, Ca, Ba, Mg, Zn)₂P₂O₇:Eu²⁺, Mn²⁺ (SPP); (Ca, Sr, Ba,Mg)₁₀(PO₄)₆(F, Cl, Br, OH): Eu²⁺, Mn²⁺; (Gd, Y, Lu, La)₂O₃:Eu³⁺, Bi³⁺;(Gd, Y, Lu, La)₂O₂S:Eu³⁺, Bi³⁺; (Gd, Y, Lu, La)VO₄:Eu³⁺, Bi³⁺; (Ca,Sr)S:Eu²⁺; SrY₂S₄: Eu²⁺; CaLa₂S₄:Ce³⁺; (Ca, Sr)S:Eu²⁺;3.5MgO*0.5MgF₂*GeO₂:Mn⁴⁺; (Ba, Sr, Ca)MgP₂O₇:Eu²⁺, Mn²⁺; (Y,Lu)₂WO₆:Eu³+, Mo⁶⁺; (Ba, Sr, Ca)_(x)Si_(y)N_(z):Eu²⁺.
 11. The lightingapparatus of claim 9, wherein said one or more additional phosphorscomprises at least one of (Sr,Ca)S:Ce³⁺,Eu²⁺; (Sr, Ba,Ca)₂Si_(5-x)Al_(x)N_(8-x)O_(x): Ce³⁺,Eu²⁺; and BaSi₇N₁₀: Ce³⁺,Eu²⁺. 12.The lighting apparatus of claim 1, wherein said phosphor compositioncomprises at least one of(Lu_(0.97)Ce_(0.03))₃Al_(4.8)Si_(0.2)O_(11.8)N_(0.2),(Lu_(0.97)Ce_(0.03))₃Al_(4.9)Si_(0.1)O_(11.9)N_(0.1),(Y_(0.97)Ce_(0.03))₃Al_(4.9)Si_(0.1)O_(11.9)N_(0.1), and(Y_(0.97)Ce_(0.03))₃Al_(4.8)Si_(0.2)O_(11.8)N_(0.2).
 13. The lightingapparatus of claim 1, wherein 0.01≦x≦0.05, 0.02≦y≦0.20, 0≦z≦0.5,0≦w≦0.5, and 4.8≦a≦5.0.
 14. A phosphor composition comprising anoxynitride phosphor comprising(RE_(1-x)Ce_(x))₃Al_(a-y-z-w)Si_(y)Ga_(z)Sc_(w)O_(12-y)N_(y), where REis at least one of Lu, Gd, Y, and Tb, 0.001≦x≦0.10, 0≦w≦2, 0.001≦y≦0.50,0≦z≦4.999, and 4.5≦a≦5.0.
 15. The phosphor composition of claim 14,wherein 0.01≦x≦0.05, 0.02≦y≦0.20, 0≦z≦0.5, 0≦w≦0.5, and 4.8≦a≦5.0. 16.The phosphor composition of claim 14, comprising at least one of(Lu_(0.97)Ce_(0.03))₃Al_(4.8)Si_(0.2)O_(11.8)N_(0.2),(Lu_(0.97)Ce_(0.03))₃Al_(4.9)Si_(0.1)O_(11.9)N_(0.1),(Y_(0.97)Ce_(0.03))₃Al_(4.9)Si_(0.1)O_(11.9)N_(0.1), and(Y_(0.97)Ce_(0.03))₃Al_(4.8)Si_(0.2)O_(11.8)N_(0.2).
 17. A phosphorblend including a first phosphor comprising an oxynitride phosphorcomposition having a formula(RE_(1-x)Ce_(x))₃Al_(a-y-z-w)Si_(y)Ga_(z)Sc_(w)O_(12-y)N_(y), where REis at least one of Lu, Gd, Y, and Tb, 0.001≦x≦0.10, 0≦w≦2, 0.001≦y≦0.50,0≦z≦4.999, and 4.5≦a≦5.0; and at least one additional phosphor, whereinthe phosphor blend is capable of emitting light suitable for use ingeneral illumination either alone or in combination with radiationemitted by a light source radiationally coupled to the phosphor.
 18. Thephosphor blend of claim 17, wherein said first phosphor comprises atleast one of (Lu_(0.97)Ce_(0.03))₃Al_(4.8)Si_(0.2)O_(11.8)N_(0.2),(Lu_(0.97)Ce_(0.03))₃Al_(4.9)Si_(0.1)O_(11.9)N_(0.1),(Y_(0.97)Ce_(0.03))₃Al_(4.9)Si_(0.1)O_(11.9)N_(0.1), and(Y_(0.97)Ce_(0.03))₃Al_(4.8)Si_(0.2)O_(11.8)N_(0.2).
 19. The phosphorblend of claim 17, wherein said at least one additional phosphorcomprises at least one of (Sr, Ca)S:Ce³⁺,Eu²⁺; (Sr, Ba,Ca)₂Si_(5-x)Al_(x)N_(8-x)O_(x): Ce³⁺,Eu²⁺; and BaSi₇N₁₀:Ce³⁺,Eu²⁺. 20.The phosphor blend of claim 17, wherein said at least one additionalphosphor comprises at least one of (Ba, Sr, Ca)₅(PO₄)₃(Cl, F, Br,OH):Eu²⁺, Sb³⁺; (Ba, Sr, Ca)MgAl10O₁₇:Eu²⁺,Mn²⁺; (Ba, Sr, Ca)BPO₅:Eu²⁺,Mn²⁺; (Sr, Ca)₁₀(PO₄)₆*nB₂O₃:Eu²⁺; 2SrO*0.84P₂O₅*0.16B₂O₃:Eu²⁺;Sr₂Si₃O_(8*2)SrCl₂:Eu²⁺; Ba₃MgSi₂O₈:Eu²⁺; Sr₄Al₁₄O₂₅:Eu²⁺;BaAl₈O₁₃:Eu²⁺; Sr₄Al₁₄O₂₅:Eu²⁺; BaAl₈O₁₃:Eu²⁺;2SrO-0.84P₂O_(5-0.16)B₂O₃:Eu²⁺; (Ba, Sr, Ca)MgAl₁₀O₁₇:Eu²⁺,Mn²⁺; (Ba,Sr, Ca, Zn)₅(PO₄)₃(Cl, F, OH):Eu²⁺, Mn²⁺, Sb³⁺; (Ba, Sr,Ca)MgAl₁₀O₁₇:Eu²⁺,Mn²⁺; (Ba, Sr, Ca)Al₂O₄:Eu²⁺; (Y, Gd, Lu, Sc,La)BO₃:Ce³⁺, Tb³⁺; Ca₈Mg(SiO₄)₄Cl₂:Eu²⁺, Mn²⁺; (Ba, Sr, Ca)₂SiO₄:Eu²⁺;(Ba, Sr, Ca)₂(Mg, Zn)Si₂O₇:Eu²⁺; (Sr, Ca, Ba)(Al, Ga, In)₂S₄:Eu²⁺; (Y,Gd, Tb, La, Sm, Pr, Lu)₃(Al, Ga)₅O₁₂:Ce³⁺; (Ca, Sr)₈(Mg, Zn)(SiO₄)₄Cl₂:Eu²⁺, Mn²⁺ (CASI); Na₂Gd₂B₂O₇:Ce³⁺, Tb³⁺; (Ba, Sr)₂(Ca, Mg, Zn)B₂O₆:K,Ce, Tb; (Sr, Ca, Ba, Mg, Zn)₂P₂O₇:Eu²⁺, Mn²⁺ (SPP); (Ca, Sr, Ba,Mg)₁₀(PO₄)₆(F, Cl, Br, OH): Eu²⁺, Mn²⁺; (Gd, Y, Lu, La)₂O₃:Eu³⁺, Bi³⁺;(Gd, Y, Lu, La)₂O₂S:Eu³⁺, Bi³⁺; (Gd, Y, Lu, La)VO₄:Eu³⁺, Bi³⁺; (Ca,Sr)S:Eu²⁺; SrY₂S₄: Eu²⁺; CaLa₂S₄:Ce³⁺; (Ca, Sr)S:Eu²⁺;3.5MgO*0.5MgF₂*GeO₂:Mn⁴⁺; (Ba, Sr, Ca)MgP₂O₇:Eu²⁺, Mn²⁺; (Y,Lu)₂WO₆:Eu³+, Mo⁶⁺; (Ba, Sr, Ca)_(x)Si_(y)N_(z):Eu²⁺.